Most oil and gas wells require some form of stimulation to enhance hydrocarbon flow to make or keep them economically viable. The servicing of oil and gas wells to stimulate production requires the pumping of fluids under high pressure. The fluids may be low temperature or caustic and are frequently abrasive because they are laden with abrasive propants such as sharp sand, bauxite or ceramic granules.
In order to protect the components which make up the wellhead, such as the valves, tubing hanger, casing hanger, casing head and blowout preventer equipment, wellhead isolation tools are used during well fracturing and well stimulation procedures. The wellhead isolation tools generally work on a principal of inserting a high-pressure mandrel through various pressure-sensitive valves and spools of the wellhead to isolate those wellhead components from elevated fluid pressures and from low temperature or corrosive and/or abrasive fluids used during the well stimulation treatment to stimulate production from the well. One example of those wellhead isolation tools is described in the Assignee's U.S. Pat. No. 6,626,245, entitled BLOWOUT PREVENTER PROTECTOR AND METHOD OF USING SAME. Another example of such a tool is described in the Assignee's U.S. Pat. No. 4,867,243, which issued Sep. 19, 1989 and is entitled WELLHEAD ISOLATION TOOL AND SETTING TOOL AND METHOD OF USING SAME. In those examples, a top end of the mandrel is connected to one or more high pressure valves through which the well stimulation fluids are pumped. A pack-off assembly is provided at a bottom end of the mandrel for achieving a fluid seal against an inside of a production tubing or well casing, so that the wellhead is completely isolated from the well stimulation fluids.
Various pack-off assemblies, commonly referred to as “cup tools”, provided at a bottom end of the mandrel of wellhead isolation tools are described in other prior art patents, such as U.S. Pat. No. 4,023,814, entitled A TREE SAVER PACKER CUP, which issued to Pitts on May 17, 1977; U.S. Pat. No. 4,111,261, entitled A WELLHEAD ISOLATION TOOL, which issued to Oliver on Sep. 5, 1978; U.S. Pat. No. 4,601,494, entitled A NIPPLE INSERT, which issued to McLeod et al. on Jul. 22, 1986; U.S. Pat. No. 5,261,487, entitled PACKOFF NIPPLE, which issued on Nov. 16, 1993 to McLeod, et al; Assignee's U.S. Pat. No. 6,918,441 entitled CUP TOOL FOR HIGH PRESSURE MANDREL which issued Jul. 19, 2005; and, Assignee's published United States Patent application 20040055742 entitled CUP TOOL FOR HIGH PRESSURE MANDREL which was published on Mar. 25, 2004. These pack-off assemblies include a cup tool and/or a packoff element that radially expands under high fluid pressures to seal against the inside wall of a production tubing or casing.
Although at least some of the prior art cup tools provide an adequate seal under most downhole conditions, they do not always provide a reliable seal in tubing or casing that is bent or out-of-round. They may also fail to provide a reliable seal when low temperature, very caustic or solvent-laden fluids are used for a well stimulation treatment. All low temperature, highly caustic and solvent-laden fluids stress the materials used to make elastomeric sealing cups and/or packoff elements used to achieve the high pressure seals. That stress can lead to seal failure, especially if a casing or tubing string into which the cup tool is inserted is not straight or is out-of-round.
There is therefore a need for a reliable cup tool for a high pressure mandrel used for injecting low temperature, caustic and/or solvent-laden well stimulation fluids.